Electric coil with a low voltage differential between adjacent windings

ABSTRACT

The present invention relates to a coil including a plurality of layers of windings wound around an axis. The layers are radial and alternately wound from the inside to the outside and from the outside to the inside.

FIELD OF INVENTION

The present invention relates to the winding of electric coils, such ashigh voltage transformer coils. The present invention more specificallyaims at a specific winding enabling to avoid insulation problems betweentwo adjacent windings of two successive layers.

BACKGROUND OF INVENTION

An electric coil generally includes axial winding layers, that is, eachlayer includes windings wound next to one another parallel to the coilaxis. Most often, the coil includes many more windings in the axialdirection than in the radial direction.

A disadvantage of such a coil is that two adjacent windings of twosuccessive layers can be separated by a large number of turns, so thatthey are submitted to a voltage differential which is too high for theinsulator of the windings, generally an enamel. Insulator layers thushave to be interposed between the layers of windings, which makes thecoil more bulky and its fabrication more complex.

To avoid this disadvantage, in European patent application 0518737, itis provided to wind the windings in oblique layers. A coil obtained bythis method has the disadvantage of being bulky since it has atrapezoidal cross-section which necessarily implies that the externaldiameter of the coil is larger, for a given number of windings, thanthat of a coil with a rectangular cross-section. The bulk of the coil isfurther increased by the fact that it includes a large number ofcrossing windings which hinder a contiguous disposition of the windings.

Due to the many winding crossings, this winding method is not applicableto conductors with a large diameter or a rectangular cross-section.

SUMMARY OF INVENTION

A device for winding coils including a plurality of layers of windingswound around an axis, the layers being radial and wound alternately froman inside to an outside and from the outside to the inside, including:internal and external winding guides distributed in a plane of a layerof windings being wound; means for enabling the external guides to beretracted from an engaged position with the internal guides so as tofollow the external diameter of a layer being wound from the inside tothe outside, and the internal guides to be retracted from an engagedposition with the external guides so as to follow the internal diameterof a layer being wound from the outside to the inside; a fixed guidingmeans to bring a conductor to be wound into the plane of the windingguides and to hold a first surface of the layer being wound; and ashifting mechanism for axially shifting a completed layer into a hopperat the side opposite the guiding means.

An object of the present invention is to provide a coil with a low bulkand avoiding insulation problems between two adjacent windings ofsuccessive layers.

To achieve this object, the present invention provides a coil includinga plurality of layers of windings wound around an axis, the layers beingradial and wound alternately from the inside to the outside and from theoutside to the inside.

According to an embodiment of the present invention, the coil conductorshave a rectangular cross-section.

According to an embodiment of the present invention, the main axis ofthe rectangular cross-section of the conductors is perpendicular to thecoil axis.

According to an embodiment of the present invention, the coil conductorshave a circular cross-section, each layer including the same number ofwindings as the preceding layer and being radially shifted with respectto the preceding layer by one conductor half-diameter.

According to an embodiment of the present invention, each winding of thecoil includes several conductors in the plane of the associated layer.

The present invention also aims at a device for winding coils of theabove-mentioned type. The device includes internal and external turningguides distributed in the plane of a layer of windings being wound. Theexternal guides are retractable from an engaged position with theinternal guides so as to follow the external diameter of a layer beingwound from the inside to the outside. The internal guides areretractable from an engaged position with the external guides so as tofollow the internal diameter of a layer being wound from the outside tothe inside. A fixed guiding means brings a conductor to be wound in theplane of the turning guides and maintains a first surface of the layerbeing wound. A mechanism is provided to perform an axial shifting of acompleted layer to a hopper on the side opposite the guiding means.

According to an embodiment of the present invention, the guiding meansand the shifting mechanism include together a plurality of rollers witha radial axis distributed on the first surface of the layer being wound,these rollers being provided to axially penetrate between the externaland internal turning guides to shift a completed layer.

According to an embodiment of the present invention, the hopper includesa plate for maintaining the wound layers at the side opposite to theguiding means, this plate being axially retractable upon pushing of eachcompleted layer.

The foregoing objects, features and advantages of the present inventionwill be discussed in detail in the following non-limiting description ofspecific embodiments in relation with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates a coil according to the presentinvention under construction;

FIGS. 2A and 2B show a front view and a side view of a layer of windingsaccording to the present invention and the starting of the next windinglayer;

FIG. 2C shows, in a side view, several winding layers according to thepresent invention, such as they are formed in practice;

FIGS. 3A-3C schematically show several alternative winding layersaccording to the present invention;

FIG. 4 shows a front view of a winding device according to the presentinvention, divided into sectors corresponding to winding steps; and

FIGS. 5A and 5B show cross-sectional side views of a portion of thedevice of FIG. 4 for two winding steps.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cylinder 10 with an axis A, around which a coil should bewound. According to the present invention, the coil is implemented inradial layers, that is, each layer includes several windingssuccessively wound in a same plane perpendicular to axis A of the coil.In FIG. 1, the winding order of the windings is indicated by increasingnumbers starting from 1.

Moreover, according to an aspect of the present invention, the layersare wound alternatively from the inside to the outside and from theoutside to the inside. For example, in FIG. 1, the first layer includesfive windings wound from the inside to the outside. After winding thelast winding 5, the first winding 6 of the following layer is wound nextto winding 5 and the following windings 7 to 10 are wound towards theinside (that is, towards axis A) starting from winding 6.

With this configuration, the number of turns separating two windings oftwo adjacent layers is lower than twice the number of windings in theradial direction. Most of the time, the ratio between the number ofwindings in the radial direction and the number of windings in the axialdirection is so low that it is no longer necessary to lay an insulatorbetween the successive layers.

Further, the cross-section of the coil obtained is rectangular and thushas an optimal bulk.

The alternate winding towards the outside and towards the inside enablesone to obtain a natural and automatic transition from one layer ofwindings to the next in such a way that the layers are contiguous.

FIGS. 2A and 2B show a front view and a side view of a first layer ofwindings according to the present invention and of the beginning of asecond layer of windings. The successive windings 1 to 5 form a spiralrather than a succession of circles, especially when the diameter of theconductor used is large. Thus, the penultimate winding 4 of the firstlayer progressively reaches, as shown in dotted lines in FIG. 2A, theexternal diameter of the coil. The last winding 5 remains in the planeof windings 1 to 4 until it reaches the point (at the bottom) wherewinding 4 starts progressively reaching the external diameter. From thispoint, winding 5 inscribes in the external diameter by progressivelypassing next to winding 4 until it ends in the plane of the second layerof windings which starts with winding 6 (at the top).

As shown in mixed lines in FIG. 2A, winding 6 inscribes in the externaldiameter by passing next to winding 5 down to the point (at the bottom)where winding 5 starts its lateral transition to the second layer. Fromthis point, winding 6 progressively shifts to the inside, whileremaining in contact with the first layer, to initiate a spiral goingprogressively to cylinder 10.

FIGS. 2A and 2B correspond to a theoretical case. The progressivetransition from winding 5 to winding 6, the beginning of which has beenshown at the bottom of FIGS. 2A and 2B, is in fact abrupt and startslater, practically at the beginning of the layer (at the top of FIGS. 2Aand 2B).

FIG. 2C illustrates several transitions from one layer to the next, suchas they appear in reality. These transitions are due to the fact thatthe space shown as empty between cylinder 10 and the end of winding 1 isin fact filled by the end of winding 1; the spiral is flattened in theupper left quadrant in FIG. 2A.

If the conductor used for winding has a rectangular cross-section, thetransitions from a layer of windings to the next can only be abrupt,even in theory. These abrupt transitions cause of course nodisadvantage, since the layers of windings remain contiguous.

FIGS. 3A-3C illustrates three practical alternatives of a coilimplemented according to the present invention.

When a conductor with a circular section is used, as shown as an examplein the preceding drawings, the windings actually tend to shift radiallyby one half-diameter from one layer to another to find a stableposition. A coil according to the present invention may then have twoalternative configurations illustrated in FIGS. 3A and 3B.

According to a first alternative, layers including a given number ofwindings are separated by layers including one winding less and shiftedby one conductor half-diameter to the outside.

According to the second alternative, the layers include the same numberof windings but they are alternately shifted to the outside and to theinside by one conductor half-diameter.

The shifting of the windings from one layer to the next causes adecrease of the axial bulk of the coil, the length of the obtained coilbeing slightly lower than the number of axial windings of the coilmultiplied by their diameter. However, this bulk reduction is notuniform since, in a certain position, each winding of a layer crossestwo windings of the preceding layer in the first alternative (FIG. 3A)or one winding of the preceding layer in the second alternative (FIG.3B). Thus, the bulk reduction does not occur in the crossing areas,which causes an irregularity of the cross-section of the coil. Thesecond alternative (FIG. 3B), which will provide a less irregularcross-section, will be preferred.

As illustrated in FIG. 3C a coil obtained by means of a conductor with arectangular cross-section is partially illustrated. With a conductorhaving a rectangular cross-section, the above-mentioned problemsdisappear. A coil with a perfectly rectangular cross-section isobtained. Preferably, as shown, the main axis of the rectangularcross-section is perpendicular to axis A of the coil. This facilitatesthe winding process at the transitions from one layer to the next.

FIG. 4 shows a device for fabricating coils with radial layers accordingto the present invention. The device is shown at four different windingsteps, numbered from 1 to 4.

The device includes a ring-shaped spacing 20 in which is wound eachradial layer of windings. This spacing 20 is limited between an externalplate 21 and an internal plate 22 located in a same plane. Externalplate 21 includes a plurality of external guides 24e distributed at theexternal circumference of ring-shaped spacing 20. The internal ends ofguides 24e are arcuate with a diameter substantially equal to theexternal diameter of ring-shaped spacing 20. Similarly, several internalguides 24i are distributed at the circumference of internal plate 22 incorrespondence with external guides 24e. The ends of guides 24i arearcuate with a diameter substantially equal to the internal diameter ofring-shaped spacing 20. Each of guides 24 is likely to slide between anopen position of ring-shaped spacing 20 and a closed position of thisspacing.

A plurality of rollers with a radial axis 26 are distributed onring-shaped spacing 20 and roll on a surface of a layer of windingsbeing wound. Of course, for rollers 26 not to be disturbed in theirrolling, the guides 24 are arranged in deep enough grooves.

In an initial step, not shown, at the beginning of the winding of alayer from the inside to the outside, the internal guides 24i areretracted radially to define the internal diameter of the layer, and theexternal guides 24e are engaged with the corresponding internal guides24i. The internal diameter may be chosen at any value, higher than thediameter of plate 22.

At step 1, plates 21, 22, and guides 24 are rotated, clockwise in FIG.4, while rollers 26 remain fixed and roll on the edges of ring-shapedspacing 20.

A conductor 28 to be wound arrives tangentially to ring-shaped spacing20 at the level of one of rollers 26 which rectifies conductor 28 tobring it in the plane of plates 21 and 22, that is, in the plane of thelayer being wound. Conductor 28 has to be rectified since, as shown in alocal view according to an arrow F, conductor 28 arrives with aninevitable angle of incidence with respect to plates 21 and 22.

As the plates turn, the windings accumulate in spacing 20 from theoutside to the inside thanks to the tension of conductor 28 and to thefact that rollers 26, in sufficient number, maintain the windings inspacing 20, preventing the winding being formed from crossing thewinding previously formed. Each time an external guide 24e passes underthe roller 26 at which arrives conductor 28, this guide 24 is pushedback to the outside by one step by the new winding being formed.

FIG. 5A illustrates a partial cross-sectional view of the device of FIG.4 at step 1. This FIG. 5A shows layers of previously wound windings,which have been piled up in a hopper located at the bottom ofring-shaped spacing 20, behind the layer being wound. These previouslywound layers are maintained against the layer being wound and againstguides 24 by a plate 30. The combined action of hopper plate 30, ofguides 24, and of rollers 26 maintains the wound layers flat.

As shown, guides 24 have a thickness lower than the diameter of theconductor to be wound, which helps rollers 26 maintain flat the layerbeing wound. The winding being wound has no other possibility thanforming radially by pushing back guide 24e. Preferably, guides 24include chamfers which help their pushing away by the winding beingformed. The previously wound layers are stored by any adequate means,for example between an internal cylinder 32i and an external cylinder32e added at the back of plates 21 and 22, and turning therewith. Suchcylinders, generally in cardboard, are currently used to manipulatelarge size coils.

In step 2 shown in FIG. 4, the last winding of the layer has just beenformed. The external diameter reached may be chosen at any value, lowerthan the internal diameter of plate 21. The layer just wound has to bepushed back into the hopper located at the back. For this purpose, forexample, the guide pairs 24i and 24e are brought in correspondence withrollers 26 and guides 24i and 24e are sufficiently spaced from oneanother to enable rollers 26 to penetrate into ring-shaped spacing 20and thus push back into the hopper the layer which has just been wound.

FIG. 5B illustrates this operation in a cross-sectional side view. Atthe same time as roller 26 pushes back the last wound layer, plate 30 ofthe hopper is of course released to enable this pushing back.

According to an alternative, plate 30 is fixed and the turning plates21, 22 and guides 24 altogether are shifted by one conductor diameter,to the right on FIG. 5B.

In step 3 shown in FIG. 4, rollers 26 have recovered their initialposition, external guides 24e are brought to a position defining theexternal diameter of the new layer, and internal guides 24i are engagedwith external guides 24e. The guides 24 so placed prevent the last woundlayer from undoing itself. To avoid its undoing as rollers 26 join theirinitial position and before guides 24 can be installed, these operationsare performed in at least two passes. In a first pass, they areperformed in the even sectors of the turning plates while the layer ismaintained in place in the odd sectors. In the second pass, theoperations are performed in the odd sectors, the layer being maintainedin the even sectors.

In step 4, a layer is being wound from the outside to the inside fromthe state of step 3. As in step 1, plates 21, 22, as well as guides 24are rotated clockwise. Each time a pair of guides 24 passes under theroller 26 at which conductor 28 is supplied, internal guide 24i ispushed back by one step to the inside by the new winding being formed.

In fact, in this winding step, the windings are wound around internalguides 24i. It can thus be remarked that a relatively large number ofinternal guides 24i should be provided to cover as best as possible theinternal diameter of ring-shaped spacing 20. Indeed, undesired straightportions always form in the windings in the sectors not covered byadjacent guides 24i.

Once the desired internal diameter is reached, the layer which has justbeen wound is pushed back into the hopper in the way described inrelation with steps 2 and 3, internal guides 24i being then positionedto determine the internal diameter of a new layer to be wound, andexternal guides 24e being brought into engagement with internal guides24i. Steps 1 to 4 are then repeated.

Preferably, all the moving components of the device are controlled byjacks, for example, pneumatic or electric jacks. By stopping the powersupply of the jacks of guides 24, the position of these guides isensured with a relatively large rigidity. At steps 1 to 4, the jackassociated with the guide which is to be pushed back by the windingbeing formed is released. The release position is determined, forexample, by a sensor which detects the coming of the roller 26 at whichconductor 28 is supplied.

Similarly, the jack of the plate of hopper 30 is moved as roller 26pushes back the last wound layer.

Many alterations and modifications of the present invention will occurto those skilled in the art. For example, if there is room between thepairs of guides 24, rollers 26 can be arranged to push back thesuccessive layers into the hopper elsewhere than at the pairs of guides24, so that these guides 24 can all be installed simultaneously whileall the rollers 26 are still in a push position. This facilitates thecontrol of the rollers and guides with respect to what has beendescribed, since all the rollers and all the guides can then becontrolled simultaneously. According to an alternative, apertures may beprovided in guides 24 so that they can be installed avoiding therollers, while the rollers are still in a push position.

Plates 21, 22, and guides 24 have been described as rotatable, rollers26 being fixed. It should be clear that plates 21, 22, and guides 24could be fixed and rollers 26 rotatable.

Of course, the present invention applies to the case where it is desiredto wind several conductors 28 at the same time. The several conductorsare then wound at the same time in a same layer.

The present invention is not limited to windings with a circularcross-section. It applies to windings with any cross-section, determinedby the movement of guides 24.

What is claimed is:
 1. A device for winding coils including a pluralityof layers of windings wound around an axis, the layers being radial andwound alternately from an inside to an outside and from the outside tothe inside, comprising:internal and external winding guides distributedin a plane of a layer of windings being wound; means for enabling theexternal guides to be retracted from an engaged position with theinternal guides so as to follow the external diameter of a layer beingwound from the inside to the outside, and the internal guides to beretracted from an engaged position with the external guides so as tofollow the internal diameter of a layer being wound from the outside tothe inside; a fixed guiding means to bring a conductor to be wound intothe plane of the winding guides and to hold a first surface of the layerbeing wound; and a shifting mechanism for axially shifting a completedlayer into a hopper at a side opposite the guiding means.
 2. A windingdevice according to claim 1, wherein the guiding means and the shiftingmechanism include together a plurality of rollers with a radial axisdistributed on said first surface of the layer being wound, theserollers being arranged to axially penetrate between the external andinternal turning guides to shift a completed layer.
 3. A winding deviceaccording to claim 1, wherein the hopper includes a plate to supportwound layers on a side opposite the guiding means, and axial retractionmeans for enabling said plate to be axially retracted upon shifting ofeach completed layer.
 4. A device according to claim 1, wherein theconductors have a rectangular cross-section.
 5. A device according toclaim 4, wherein the main axis of the rectangular cross-section of theconductors is perpendicular to the axis (A) of the coils.
 6. A deviceaccording to claim 1, wherein the conductors have a circularcross-section, each layer including the same number of windings as thepreceding layer and being radially shifted with respect to the precedinglayer by one conductor half-diameter.
 7. A device according to claim 1,wherein each winding includes several conductors in the plane of theassociated layer.
 8. A device for winding coils including a plurality oflayers of windings wound around an axis, the layers being radial andwound alternately from an inside to an outside and from the outside tothe inside, comprising:internal and external winding guides distributedin a plane of a layer of windings being wound; means for enabling theexternal guides to be shifted from an engaged position with the internalguides so as to follow the external diameter of a layer being wound fromthe inside to the outside, and the internal guides to be shifted from anengaged position with the external guides so as to follow the internaldiameter of a layer being wound from the outside to the inside; and, aplurality of rollers to bring a conductor to be wound into the plane ofthe winding guides, support a first surface of the layer being wound,and axially shift a completed layer.